I would think that a visual day/night cycle is pretty much a gimme. It's easy enough to change the lighting and shaders based on the clock that I don't see how they could not do it.

Beyond that....? I'm not expecting much, honestly. Seasons would be nice, but GF already has their hands full with doing one 3D overworld, and I don't think it's likely that they'll do four. Maybe, and it'd be nice if they managed to pull it off well, but I just don't think it's going to happen. Maybe after they get these two out of the way and get a better idea of the ins and outs of developing for the 3DS.